Substrate structures for integrated series connected photovoltaic arrays and process of manufacture of such arrays

ABSTRACT

The invention comprises deposition of thin film photovoltaic junctions on metal foil substrates which can be heat treated following deposition in a continuous fashion without deterioration of the metal support structure. In a separate operation, an interconnection substrate structure is produced in a continuous roll-to-roll fashion. The metal foil supported photovoltaic junction is then laminated to the interconnecting substrate structure and conductive connections are deposited to complete the array. In this way the interconnection substrate structure can be uniquely formulated from polymer-based materials since it does not have to endure high temperature exposure. Furthermore, the photovoltaic junction and its metal foil support can be produced in bulk without the need to use the expensive and intricate material removal operations currently taught in the art to achieve series interconnections.

This application is a Continuation-in-Part of application Ser. No.08/441,552, filed May 15, 1995, now U.S. Pat. No. 5,547,516.

BACKGROUND OF THE INVENTION

Photovoltaic cells have developed according to two distinct methods. Theinitial operational cells employed a matrix of single crystal siliconappropriately doped to produce a planar p-n junction. An intrinsicelectric field established at the p-n junction produces a voltage bydirecting solar photon produced holes and free electrons in oppositedirections. Despite good conversion efficiencies and long-termreliability, widespread energy collection using single-crystal siliconcells is thwarted by the exceptionally high cost of single crystalsilicon material and interconnection processing.

A second approach to produce photovoltaic cells is by depositing thinphotovoltaic semiconductor films on a supporting substrate. Materialrequirements are minimized and technologies can be proposed for massproduction. The thin film structures can be designed according to dopedhomojunction technology such as that involving silicon films, or canemploy heterojunction approaches such as those using CdTe orchalcopyrite materials.

Despite significant improvements in individual cell conversionefficiencies for both single crystal and thin film approaches,photovoltaic energy collection has been generally restricted toapplications having low power requirements. One factor impedingdevelopment of bulk power systems is the problem of economicallycollecting the energy from an extensive collection surface. Photovoltaiccells can be described as high current, low voltage devices. Typicallyindividual cell voltage is less than one volt. The current component isa substantial characteristic of the power generated. Efficient energycollection from an expansive surface must minimize resistive lossesassociated with the high current characteristic. A way to minimizeresistive losses is to reduce the size of individual cells and connectthem in series. Thus, voltage is stepped through each cell while currentand associated resistive losses are minimized.

It is readily recognized that making effective, durable seriesconnections among multiple small cells can be laborious, difficult andexpensive. In order to approach economical mass production of seriesconnected arrays of individual cells, a number of factors must beconsidered in addition to the type of photovoltaic materials chosen.These include the substrate employed and the process envisioned. Sincethin films can be deposited over expansive areas, thin film technologiesoffer additional opportunities for mass production of interconnectedarrays compared to inherently small, discrete single crystal siliconcells. Thus a number of U.S. patents have issued proposing designs andprocesses to achieve series interconnections among the thin filmphotovoltaic cells. Many of these technologies comprise deposition ofphotovoltaic thin films on glass substrates followed by scribing to formsmaller area individual cells. Multiple steps then follow toelectrically connect the individual cells in series array. Examples ofthese proposed processes are presented in U.S. Pat. Nos. 4,443,651,4,724,011, and 4,769,086 to Swartz, Turner et al. And Tanner et al.respectively. While expanding the opportunities for mass production ofinterconnected cell arrays compared with single crystal siliconapproaches, glass substrates must inherently be processed on anindividual batch basis.

More recently, developers have explored depositing wide area films usingcontinuous roll-to-roll processing. This technology generally involvesdepositing thin films of photovoltaic material onto a continuouslymoving web. However, a challenge still remains regarding subdividing theexpensive films into individual cells followed by interconnecting into aseries connected array. For example, U.S. Pat. No. 4,965,655 to Grimmeret. al. and U.S. Pat. No. 4,697,041 to Okamiwa teach processes requiringexpensive laser scribing and interconnections achieved with laser heatstaking. In addition, these two references teach a substrate of thinvacuum deposited metal on films of relatively expensive polymers. Theelectrical resistance of thin vacuum metallized layers significantlylimits the active area of the individual interconnected cells.

It has become well known in the art that the efficiencies of certainpromising thin film photovoltaic junctions can be substantiallyincreased by high temperature treatments. These treatments involvetemperatures at which even the most heat resistant plastics suffer rapiddeterioration, thereby requiring either ceramics, glass, or metalsubstrates to support the thin film junctions. Use of a glass or ceramicsubstrate generally restricts one to batch processing and handlingdifficulty. Use of a metal foil as a substrate allows continuousroll-to-roll processing. However, despite the fact that use of a metalfoil allows high temperature processing in roll-to-roll fashion, thesubsequent interconnection of individual cells effectively in aninterconnected array has proven difficult, in part because the metalfoil substrate is electrically conducting.

U.S. Pat. No. 4,747,618 to Nath et al. teaches a design and process toachieve interconnected arrays using roll-to-roll processing of a metalweb substrate such as stainless steel. The process includes multipleoperations of cutting, selective deposition, and riveting. Theseoperations add considerably to the final interconnected array cost.

U.S. Pat. No. 5,385,848 to Grimmer teaches roll-to-roll methods toachieve integrated series connections of adjacent thin film photovoltaiccells supported on an electrically conductive metal substrate. Theprocess includes mechanical or chemical etch removal of a portion of thephotovoltaic semiconductor and transparent top electrode to expose aportion of the electrically conductive metal substrate. The exposedmetal serves as a contact area for interconnecting adjacent cells. Thesematerial removal techniques are troublesome for a number of reasons.First, many of the chemical elements involved in the best photovoltaicsemiconductors are expensive and environmentally unfriendly. Thisremoval subsequent to controlled deposition involves containment, dustand did collection and disposal, and possible cell contamination. Thisis not only wasteful but considerably adds to expense. Secondly, theremoval processes are difficult to control dimensionally. Thus asignificant amount of the valuable photovoltaic semiconductor is lost tothe removal process. Ultimate module efficiencies are furthercompromised in that the spacing between adjacent cells grows, therebyreducing the effective active collector area for a given module area.

Thus there remains a need for an inexpensive manufacturing process whichallows high heat treatment for thin film photovoltaic junctions whilealso offering unique means to achieve effective integrated seriesconnections.

In a somewhat removed segment of technology, a number of electricallyconductive fillers have been used to produce electrically conductivepolymeric materials. This technology generally involves mixing of theconductive filler into the polymer resin prior to fabrication of thematerial into its final shape. Conductive fillers typically consist ofhigh aspect ratio particles such as metal fibers, metal flakes, orhighly structured carbon blacks, with the choice based on a number ofcost/performance considerations.

Electrically conductive resins have been used as bulk thermoplasticcompositions, or formulated into paints. Their development has beenspurred in large part by electromagnetic radiation shielding and staticdischarge requirements for plastic components used in the electronicsindustry. Other known applications include resistive heating fibers andbattery components.

In yet another separate technological segment, electroplating on plasticsubstrates has been employed to achieve decorative effects on items suchas knobs, cosmetic closures, faucets, and automotive trim. ABS(acrylonitrile-butadiene-styrene) plastic dominates as the substrate ofchoice for most applications because of a blend of mechanical andprocess properties and ability to be uniformly etched. The overallplating process comprises many steps. First, the plastic substrate ischemically etched to microscopically roughen the surface. This isfollowed by depositing an initial metal layer by chemical reduction.This initial metal layer is normally copper or nickel of thicknesstypically one-half micrometer. The object is then electroplated withmetals such as bright nickel and chromium to achieve the desiredthickness and decorative effects. The process is very sensitive toprocessing variables used to fabricate the plastic substrate, limitingapplications to carefully molded parts and designs. In addition, themany steps employing harsh chemicals make the process intrinsicallycostly and environmentally difficult. Finally, the sensitivity of ABSplastic to liquid hydrocarbons has prevented certain applications. Theconventional technology for electroplating on plastic (etching, chemicalreduction, electroplating) has been extensively documented and discussedin the public and commercial literature. See, for example, Saubestre,Transactions of the Institute of Metal Finishing, 1969, Vol. 47., orArcilesi et al., Products Finishing, March 1984.

Many attempts have been made to simplify the process of electroplatingon plastic substrates. Some involve special chemical techniques toproduce an electrically conductive film on the surface. Typical examplesof this approach are taught by U.S. Pat. No. 3,523,875 to Minklei, U.S.Pat. No. 3,682,786 to Brown et. al., and U.S. Pat. No. 3,619,382 toLupinski. The electrically conductive film produced was thenelectroplated.

Another approach proposed to simplify electroplating of plasticsubstrates is incorporation of electrically conductive fillers into theresin to produce an electrically conductive plastic. The electricallyconductive resin is then electroplated. Examples of this approach arethe teachings of Adelman in U.S. Pat. No. 4,038,042 and Luch in U.S.Pat. No. 3,865,699. Adelman taught incorporation of conductive carbonblack into a polymeric matrix to achieve electrical conductivityrequired for electroplating. The substrate was pre-etched to achieveadhesion of the subsequently electrodeposited metal. Luch taughtincorporation of small amounts of sulfur into polymer-based compoundsfilled with conductive carbon black. The sulfur was shown to have twoadvantages. First, it participated in formation of a chemical bondbetween the polymer-based substrate and an initial Group VIII basedmetal electrodeposit. Second, the sulfur increased lateral growth of theGroup VIII based metal electrodeposit over the surface of the substrate.

Since the polymer-based compositions taught by Luch could beelectroplated directly without any pretreatments, they could beaccurately defined as directly electroplateable resins (DER). Directlyelectroplateable resins, (DER), are characterized by the followingfeatures.

(a) having a polymer matrix;

(b) presence of carbon black in amounts sufficient for the overallcomposition to have an electrical volume resistivity of less than 1000ohm-cm., e.g., 100 ohm-cm., 10 ohm-cm., 1 ohm-cm.;

(c) presence of sulfur (including any sulfur provided by sulfur donors)in amounts greater than about 0.1% by weight of the overallpolymer-carbon-sulfur composition; and

(d) presence of the polymer, carbon and sulfur in said directlyelectroplateable composition of matter in cooperative amounts requiredto achieve direct, uniform, rapid and adherent coverage of saidcomposition of matter with an electrodeposited Group VIII metal or GroupVIII metal-based alloy.

The minimum workable level of carbon black required to achieveelectrical resistivities less than 1000 ohm-cm. appears to be about 8weight percent based on the weight of polymer plus carbon black.

Polymers such as polyvinyls, polyolefins, polystyrenes, elastomers,polyamides, and polyesters are suitable for a DER matrix, the choicegenerally being dictated by the physical properties required.

In order to eliminate ambiguity in terminology of the presentspecification and claims, the following definitions are supplied.

"Metal-based" refers to a material having metallic properties comprisingone or more elements, at least one of which is an elemental metal.

"Metal-based alloy" refers to a substance having metallic properties andbeing composed of two or more elements of which at least one is anelemental metal.

"Polymer-based" refers to a substance composed, by volume, of 50 percentor more hydrocarbon polymer.

"Group VIII-based" refers to a metal (including alloys) containing, byweight, 50% to 100% metal from Group VIII of the Periodic Table ofElements.

It is important to note that electrical conductivity alone isinsufficient to permit a plastic substrate to be directly electroplated.The plastic surface must be electrically conductive on a microscopicscale. For example, simply loading a small volume percentage of metalfibers may impart conductivity on a scale suitable for electromagneticradiation shielding, but the fiber separation would likely preventuniform direct electroplating. In addition, many conductivethermoplastic materials form a non-conductive surface skin duringfabrication, effectively eliminating the surface conductivity requiredfor direct electroplating.

OBJECTS OF THE INVENTION

An object of the invention is to eliminate the deficiencies in the priorart methods of producing expansive area, series interconnectedphotovoltaic arrays. A further object of the present invention is toprovide improved substrates to achieve series interconnections amongexpansive thin film cells. A further object of the invention is topermit inexpensive production of high efficiency, heat treated thin filmphotovoltaic cells while simultaneously permitting the use of polymerbased substrate materials and associated processing to effectivelyinterconnect those cells. A further object of the present invention isto provide improved processes whereby expansive area, seriesinterconnected photovoltaic arrays can be economically mass produced.

Other objects and advantages will become apparent in light of thefollowing description taken in conjunction with the drawings andembodiments.

SUMMARY OF THE INVENTION

The current invention provides a solution to the stated need byproducing the active photovoltaic film and interconnecting substrateseparately and subsequently combining them to produce the desiredexpansive series interconnected array. The invention contemplatesdeposition of thin film photovoltaic junctions on metal foil substrateswhich can be heat treated following deposition in a continuous fashionwithout deterioration of the metal support structure. In a separateoperation, an interconnection substrate structure is produced in acontinuous roll-to-roll fashion. The metal foil supported photovoltaicjunction is then laminated to the interconnecting substrate structureand conductive connections are deposited to complete the array. In thisway the interconnection substrate structure can be uniquely formulatedfrom polymer-based materials since it does not have to endure hightemperature exposure. Furthermore, the photovoltaic junction and itsmetal foil support can be produced in bulk without the need to use theexpensive and intricate material removal operations currently taught inthe ad to achieve series interconnections.

BRIEF DESCRIPTION OF THE DRAWINGS

The various factors and details of the structures and manufacturingmethods of the present invention are hereinafter more fully set forthwith reference to the accompanying drawings wherein:

FIG. 1 is a top plan view of a thin film photovoltaic cell deposited ona support foil.

FIG. 2 is a sectional view taken substantially along the line 2--2 ofFIG. 1.

FIG. 3 is an expanded sectional view showing a form of the structure oflayer of FIG. 2.

FIG. 4 illustrates a process for producing the structure shown in FIGS.1 through 3.

FIG. 5 is a sectional view illustrating the problems associated withmaking series connections among thin film photovoltaic cells shown inFIGS. 1-3.

FIG. 6 is a top plan view of a substrate structure for achieving seriesinterconnections of thin film photovoltaic cells.

FIG. 7 is a sectional view taken substantially along the line 7--7 ofFIG. 6.

FIG. 8 is a sectional view similar to FIG. 7 showing an alternateembodiment of a substrate structure for achieving seriesinterconnections of thin film photovoltaic cells.

FIG. 9 is a top plan view of an alternate embodiment of a substratestructure for achieving series interconnections of thin filmphotovoltaic cells.

FIG. 10 is a sectional view similar to FIGS. 7 and 8 taken substantiallyalong line 10--10 of FIG. 9.

FIG. 11 is a top plan view of another embodiment of a substratestructure for achieving series interconnections of thin filmphotovoltaic cells.

FIG. 12 is a sectional view taken substantially along the line 12--12 ofFIG. 11.

FIGS. 13a and 13b schematically depict a process for laminating the foilsupported thin film photovoltaic structure of FIGS. 1 through 3 to aninterconnecting substrate structure. FIG. 13a is a side view of theprocess. FIG. 13b is a sectional view taken substantially along line13b--13b of FIG. 13a.

FIGS. 14a, 14b, and 14c are views of the structures resulting from thelaminating process of FIGS. 13 and using the substrate structure ofFIGS. 7, 8 and 10, respectively.

FIGS. 15a, 15b, and 15c are sectional views taken substantially alongthe lines 15a--15a, 15b--15b, and 15c--15c of FIGS. 14a, 14b, and 14c,respectively.

FIG. 16 is a top plan view of the structure resulting from thelaminating process of FIG. 13 and using the substrate structure of FIGS.11 and 12.

FIG. 17 is a sectional view taken substantially along the line 17--17 ofFIG. 16.

FIG. 18 is a top plan view of the structures of FIGS. 14a and 15a butfollowing an additional step in manufacture of the interconnected cells.

FIG. 19 is a sectional view taken substantially along the line 19--19 ofFIG. 18.

FIG. 20 is a top plan view of a completed interconnected array.

FIG. 21 is a sectional view taken substantially along line 21--21 ofFIG. 20.

FIG. 22 is a sectional view similar to FIG. 15a but showing an alternatemethod of accomplishing the mechanical and electrical joining of thelamination process of FIG. 13.

FIG. 23 is a sectional view similar to FIG. 15a but showing an alternateembodiment of the laminated structure.

FIG. 24 is a sectional view of an alternate embodiment.

FIG. 25 is a sectional view of the embodiment of FIG. 24 after a furtherprocessing step.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. In the drawings, like reference numerals designate identicalor corresponding pads throughout several views and an additional letterdesignation is characteristic of a particular embodiment.

Referring to FIG. 1, a thin film photovoltaic cell, supported on ametal-based foil is generally indicated by 10. Structure 10 has a widthX-10 and length Y-10. Width X-10 defines a first photovoltaic cellterminal edge 45 and second photovoltaic cell terminal edge 46. It iscontemplated that length Y-10 is considerably greater than width X-10and length Y-10 can generally be described as "continuous" or being ableto be processed in a roll-to-roll fashion. FIG. 2 shows that structure10 comprises a thin film photovoltaic structure 11 supported bymetal-based foil 12. Foil 12 has first surface 65, second surface 66,and thickness "Z". Metal-based foil 12 may be of uniform composition ormay comprise a laminate of two or more metal-based layers. For example,foil 12 may comprise a base layer of inexpensive and processable metal13 with an additional metal-based layer 14 disposed between base layer13 and photovoltaic structure 11. The additional metal-based layer maybe chosen to ensure good ohmic contact between the top surface 65 ofsupport 12 and photovoltaic structure 11. Bottom surface 66 of foilsupport 12 may comprise a material 75 chosen to achieve good electricaland mechanical joining characteristics to the substrate as will beshown. The thickness Z of support layer 12 is generally contemplated tobe between 0.001 cm. and 0.025 cm. This thickness would provide adequatehandling strength while still allowing flexibility for roll-to-rollprocessing.

Photovoltaic structure 11 can be any of the thin film structures knownin the art. In its simplest form, the photovoltaic cell combines ann-type semiconductor with a p-type semiconductor to form an n-pjunction. Most often an optically transparent window electrode such as athin film of zinc or tin oxide is employed to minimize resistive lossesinvolved in current collection. FIG. 3 illustrates an example of atypical photovoltaic cell structure in section. In FIG. 3, 15 representsa thin film of a p-type semiconductor, 16 a thin film of n-typesemiconductor and 17 the resulting photovoltaic junction. Windowelectrode 18 completes the typical photovoltaic structure. The exactnature of the photovoltaic structure 11 does not form the subject matterof the present invention.

FIG. 4 refers to the method of manufacture of the foil supportedphotovoltaic structures generally illustrated in FIGS. 1 through 3. Themetal-based support foil 12 is moved in the direction of its length Ythrough a deposition process, generally indicated as 19. Process 19accomplishes deposition of the active photovoltaic structure ontosupport foil 12. Support foil 12 is unwound from supply roll 20a, passedthrough deposition process 19 and rewound onto takeup roll 2Ob. Process19 can comprise any of the processes well-known in the and fordepositing thin film photovoltaic structures. These processes includeelectroplating, vacuum sputtering, and chemical deposition. Process 19may also include treatments, such as heat treatments, intended toenhance photovoltaic cell performance.

Referring now to FIG. 5, there are illustrated cells 10 as shown in FIG.2. The cells have been positioned to achieve spacial positioning on thesupport substrate 21. Support structure 21 is by necessitynon-conductive at least in that distance indicated by numeral 70separating the adjacent cells 10. This insulating space prevents shodcircuiting from metal foil electrode 12 of one cell to foil electrode 12of an adjacent cell. In order to achieve series connection, electricalcommunication must be made from the top surface of window electrode 18to the foil electrode 12 of an adjacent cell. This communication isshown in the FIG. 5 as a metal wire 41. Metal wire 41 is clearlyimpractical for inexpensive continuous production and is shown forillustration purposes only.

It should be noted that foil electrode 12 is relatively thin, on theorder of 0.001 cm to 0.025 cm. Therefore connecting to its edge asindicated in FIG. 5 would be impractical.

Referring now to FIGS. 6 and 7, one embodiment of the substratestructures of the current invention is generally indicated by 22. Unitof substrate 22 comprises electrically conductive sheet 23 andelectrically insulating joining portion 25. 25. Electrically conductivesheet 23 has a top surface 26, bottom surface 28, width X-23, lengthY-23 and thickness Z-23. Width X-23 defines a first terminal edge 29 anda second terminal edge 30 of conductive sheet 23. Top surface 26 ofconductive sheet 23 can be thought of as having top collector surface 47and top contact surface 48 separated by imaginary insulating boundary49. The purpose for these definitions will become clear in thefollowing.

Electrically conductive sheet 23 includes an electrically conductivepolymer. Typically, electrically conductive polymers exhibit bulkresistivity values of less than 1000 ohm-cm. Resistivities less than1000 ohm-cm can be readily achieved by compounding well-known conductivefillers into a polymer matrix binder.

The substrate unit 22 may be fabricated in a number of different ways.Electrically conductive sheet 23 can comprise an extruded film ofelectrically conductive polymer joined to a strip of compatibleinsulating polymer 25 at or near terminal edge 29 as illustrated in FIG.7. Alternatively, the conductive sheet may comprise a strip ofelectrically conductive polymer 23a laminated to an insulating supportstructure 31 as illustrated in section in FIG. 8. In FIG. 8,electrically insulating joining portions 25a are simply those portionsof insulating support structure 31 not overlaid by sheets 23a.

It is contemplated that electrically conductive sheets 23 may comprisematerials in addition to the electrically conductive polymer. Forexample, a metal may be electrodeposited onto the electricallyconductive polymer for increased conductivity. In this regard, the useof a directly electroplateable resin (DER) may be particularlyadvantageous.

A further embodiment of fabrication of substrate unit 22 is illustratedin FIGS. 9 and 10. In FIG. 9, electrically conductive sheet 23bcomprises electrically conductive polymer impregnated into a fabric orweb 32. A number of known techniques can be used to achieve suchimpregnation. Insulating joining portion 25b in FIG. 9 is simply anun-impregnated extension of the web 32. Fabric or web 32 can be selectedfrom a number of woven or non-woven fabrics, including non-polymericmaterials such as fiberglass.

Referring now to FIG. 11, an alternate embodiment for the substratestructures of the present invention is illustrated. In the FIG. 11, asupport web or film 33 extends among and supports multiple individualcell units, generally designated by repeat structure 34. Electricallyconductive sheets 35 are analogous to sheet 23 of FIGS. 6 through 10. Atthe stage of overall manufacture illustrated in FIG. 11, electricallyconductive sheets 35 need not comprise an electrically conductivepolymer as do sheets 23 of FIGS. 6 through 10. However, as will beshown, electrically conducting means, typically in the form of anelectrically conductive polymer containing adhesive, must eventually beutilized to join photovoltaic laminate 10 to the top surface 50 ofelectrically conductive sheets 35. In addition, the electricallyconducting sheets 35 must be attached to the support carrier 33 withintegrity required to maintain positioning and dimensional control. Thisis normally accomplished with an adhesive, indicated by layer 36 of FIG.12.

Conductive sheets 35 are shown in FIGS. 11 and 12 as having length Y-35,width X-35 and thickness Z-35. It is contemplated that length Y-35 isconsiderably greater than width X-35 and length Y-35 can generally bedescribed as "continuous" or being able to be processed in roll-to-rollfashion. Width X-35 defines a first terminal edge 53 and second terminaledge 54 of sheet 35.

It is important to note that the thickness of the conductive sheets 35,Z-35 must be sufficient to allow for continuous lamination to thesupport web 33. Typically when using metal based foils for sheets 35,thickness between 0.001 cm and 0.025 cm would be chosen.

As with the substrate structures of FIGS. 6 through 10, is helpful tocharacterize top surface 50 of conductive sheets 35 as having a topcollector surface 51 and a top contact surface 52 separated by animaginary insulating barrier 49.

Referring now to FIGS. 13a and 13b, a process is shown for laminatingthe metal-based foil supported thin film photovoltaic structure of FIGS.1 through 3 to the substrate structures taught in FIGS. 6 through 12. InFIGS. 13a and 13b, photovoltaic cell structures as illustrated in FIGS.1 through 3 are indicated by numeral 10. Substrate structures as taughtin the FIGS. 6 through 12 are indicated by the numeral 22. Numeral 42indicates a film of electrically conductive adhesive intended to joinelectrically conductive metal-based foil 12 of FIGS. 1 through 3 toelectrically conductive sheet 23 of FIGS. 6 through 10 or electricallyconductive sheets 35 of FIGS. 11 and 12. It will be appreciated by thoseskilled in the art that the adhesive strip 42 shown in FIGS. 13a and 13bis one of but a number of appropriate metal joining techniques whichwould maintain required ohmic communication. For example, it iscontemplated that methods such as doctor blading a conductive resinprior to lamination, spot welding, soldering, joining with low melttemperature alloys, or crimped mechanical contacts would serve asequivalent methods to accomplish the ohmic joining illustrated asachieved in FIGS. 13a and 13b with a strip of conductive adhesive. Theseequivalent methods can be generically referred to as conductive joiningmeans.

Referring now to FIGS. 14 and 15, there is shown the result of thelamination process of FIG. 13 using the substrate structure of FIGS. 6through 10. FIGS 14a and 15a correspond to the substrate structures ofFIGS. 6 and 7. FIGS. 14b and 15b correspond to the substrate structureof FIG. 8. FIGS. 14c and 15c correspond to the substrate structures ofFIGS. 9 and 10. In the FIGS. 15a, 15b, and 15c, electrically conductiveadhesive layer 42 is shown as extending completely and contacting theentirety of the second surface 66 of metal-based foil supportedphotovoltaic cells 10. This complete surface coverage is not arequirement however, in that foil 12 is highly conductive and able todistribute current over the expansive width X-10 with minimal resistancelosses. For example, the structure of FIG. 22 shows an embodimentwherein electrical communication is achieved between conductive sheet 23of FIGS. 6 and 7 and second surface 66 of foil 12 through a narrow beadof conductive joining means 61. An additional bead of adhesive shown inFIG. 22 by 44, may be used to ensure spacial positioning and dimensionalsupport for this form of structure. Adhesive 44 need not be electricallyconductive.

In the FIGS. 15a, 15b, and 15c, the conductive sheets 23, 23a, and 23bare shown to be slightly greater in width X-23 than the width of foilX-10. As is shown in FIG. 23, this is not a requirement for satisfactorycompletion of the series connected arrays. FIG. 23 is a sectional viewof a form of the substrate structures of FIGS. 6 and 7 laminated by theprocess of FIG. 13 to the photovoltaic structures of FIGS. 1-3. In FIG.23, width X-10 is greater than width X-23. Electrical communication isachieved through conductive joining means 42 and additional joiningmeans 44 to achieve dimensional stability may be employed. The onlyrequirement of the current invention is that first conductive sheetterminal edge 29 be offset from first photovoltaic cell terminal edge 45to expose a portion of top surface 26 of conductive sheet 23.

Referring now to FIGS. 16 and 17, there is shown an alternate structureresulting from the laminating process of FIG. 13 as applied to thephotovoltaic cells of FIGS. 1-3 and the substrate structure of FIGS. 11and 12. In a fashion similar to that of FIGS. 15, 22, and 23, the firstterminal edges 53 of conductive sheets 35 supported by insulatingsubstrate 33 are slightly offset from the first terminal edge 45 ofphotovoltaic cells 10. This offset exposes a portion of top surface 50of conductive sheet 35. Electrical and mechanical joining of sheets 35with second surface 66 of metal-based foil 12 is shown in FIG. 17 asbeing achieved with conductive adhesive 42 as in previous embodiments.However, it is contemplated as in previous embodiments that thiselectrical and mechanical joining can be accomplished by alternate meanssuch as soldering, joining with compatible low melting point alloys,spot welding, or mechanical crimping.

Comparing the sectional views of FIGS. 15, 22, 23, and 17, one observesmany similarities. The most important common structural similarity isthat the first terminal edges 29 of conductive sheets 23 be offsetslightly from first terminal edge 45 of photovoltaic cells 10 (FIGS. 15,22, 23). Similarly, first terminal edges 53 of conductive sheets 35 areslightly offset from first terminal edges 45 of photovoltaic cells 10(FIG. 17). As will be shown, the resulting exposed top surface portionsare used as contact surfaces for the final interconnected array.

It should also be observed that the structures equivalent to those shownin FIGS. 16 and 17 can also be achieved by first joining photovoltaiccells 10 and conductive sheets 35 with suitable electrically conductivejoining means 42 to give the structure shown in FIG. 24 and laminatingthese strips to an insulating support web 33. An example of such anequivalent structure is shown in FIG. 25, wherein the laminates of FIG.24 have been adhered to insulating web 33 in defined repeat positionswith adhesive means 57. As mentioned above and as shown in FIGS. 24 and25, conductive sheets 35 do not have to contact the whole of the bottomsurface 66 of photovoltaic cell 10.

Referring now to FIGS. 18 and 19, beads 56 and 60 of insulating materialhaving been applied to the first and second terminal edges 45 and 46respectively of photovoltaic cells 10. While these beads 56 and 60 areshown as applied to the structure of FIG. 15a, it is understood thatappropriate beads of insulating material are also envisioned as asubsequent manufacturing step for the structures of 15b, 15c, 17, 22, 23and 25. The purpose of the insulating beads is to protect the edge ofthe photovoltaic cells from environmental and electrical deterioration.In addition, as will be shown the insulating bead allows for electricalinterconnections to be made among adjacent cells without electricalshorting.

It is noted that the application of insulating material 56 to firstterminal edge 45 of photovoltaic cells 10 effectively divides the topsurfaces 26 and 50 of conductive sheets 23 and 35 respectively into tworegions. The first region (region 48 of surface 26 or region 52 ofsurface 50) can be considered as a contact region for seriesinterconnects among adjacent cells. The second region (region 47 ofsurface 26 or region 51 of surface 50) can be considered as the contactregion for interconnecting the substrate to the second surface 66 ofphotovoltaic cells 10.

Referring now to FIGS. 20 and 21, there is shown the method of formingthe final interconnected array. Grid fingers 58 of a highly electricallyconductive material are deposited to achieve electrical communicationbetween the top surface 59 of the photovoltaic cell 10 and the remainingexposed contact regions 48 or 52 of an adjacent cell. It is contemplatedthat these fingers can be deposited by any of a number of processes todeposit metal containing or metal-based foils or films, including maskedvacuum deposition, printing of conductive inks, electrodeposition orcombinations thereof.

Following deposition of the grid fingers, it would be normal to protectthe integrated array with some form of encapsulant, but these latterprocesses do not form the subject matter of the present invention.

It is important to recognize that the unique design and process taughtby the present invention is accomplished in a fully additive fashion. Nowasteful and costly material removal steps are needed to achieve theintegrated series connected arrays taught. This is a significantadvantage over the prior art.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications,alternatives and equivalents may be included without departing from thespirit and scope of the inventions, as those skilled in the art willreadily understand. Such modifications, alternatives and equivalents areconsidered to be within the purview and scope of the invention andappended claims.

What is claimed is:
 1. An intermediate article in the manufacture of aseries interconnected array of photovoltaic cells comprising one or moreunits, each of said units comprising:a photovoltaic cell comprising thinfilms of semiconductor material forming a photovoltaic junctionsupported on a metal-based foil, said cell having a top cell surface anda bottom cell surface, said cell further having a cell length,a cellwidth, and a cell thickness, said cell width defining a first cellterminal edge and a second cell terminal edge, a separately preparedsubstrate structure comprising electrically conductive material andelectrically non-conductive material, said electrically conductivesubstrate material having a top surface and a linear dimension whoseendpoints define first and second terminal edges of said electricallyconductive substrate material, said electrically conductive andnon-conductive materials being joined together in a generally planarstructure, said photovoltaic cell being joined to said substratestructure such that said first cell terminal edge is positioned betweensaid first and second terminal edges of said electrically conductivesubstrate material so that a portion of said bottom cell surfaceoverlays a first portion of said conductive substrate material topsurface leaving a second portion of said conductive substrate materialtop surface exposed.
 2. The article of claim 1 wherein said cell widthis substantially constant throughout the entire length of said cell. 3.The article of claim 1 wherein said cell length is substantially greaterthan said cell width thereby allowing roll-to-roll processing.
 4. Thearticle of claim 1 wherein said bottom cell surface and said firstportion of said conductive substrate material top surface areelectrically connected by electrically conductive joining means.
 5. Thearticle of claim 4 wherein said electrically conductive joining meanscomprises an electrically conductive adhesive.
 6. The article of claim 4wherein said electrically conductive joining means comprises ametal-based solder.
 7. The article of claim 3 wherein said electricallyconductive joining means comprises a weld.
 8. The article of claim 7wherein said weld is a spot weld.
 9. The article of claim 1 furthercomprising a first said unit and a second said unit, and means toestablish electrical communication between said second exposed portionof said conductive substrate material top surface of said first unit andsaid top cell surface of said second unit.
 10. The article of claim 9wherein said means to establish electrical communication comprises anelectrodeposited metal.
 11. The article of claim 1 wherein saidmetal-based foil has a thickness, said foil thickness being between0.001 cm. and 0.025 cm.
 12. An intermediate article in the manufactureof a series interconnected array of photovoltaic cells comprising one ormore units, each of said units comprising:a substrate structurecomprising an electrically conductive portion joined to an electricallynon-conductive portion, said electrically conductive portion having topand bottom electrically conductive surfaces, a first photovoltaic cellcomprising thin films of semiconductor material forming a photovoltaicjunction supported on a metal-based foil,said foil being in electricalcommunication with said electrically conductive portion, a part of saidsubstrate top electrically conductive surface being exposed, and a partof said substrate bottom electrically conductive surface being exposed.13. An intermediate article in the manufacture of a seriesinterconnected array of photovoltaic cells comprising one or more units,each of said units comprising:a photovoltaic cell comprising thin filmsof semi-conductor forming a photovoltaic junction supported on a firstmetal-based foil having a first metal-based foil thickness, said cellhaving a top cell surface and a bottom cell surface, said cell furtherhaving a cell length, a cell width and a cell thickness, said cell widthdefining a first cell terminal edge and a second cell terminal edge, anoriginally separate second metal-based foil characterized by the absenceof semiconductor materials, said second metal-based foil having a lengthco-linear with said cell length, a width co-linear with said cell width,and a thickness, said second metal-based foil width defining first andsecond terminal edges of said second metal-based foil, said secondmetal-based foil further having top and bottom surfaces, saidphotovoltaic cell being positioned relative to said second metal-basedfoil such that said first cell terminal edge is positioned between saidfirst and second terminal edges of said second metal-based foil so thata portion of said bottom cell surface overlays a first portion of saidsecond metal-based foil top surface leaving a second portion of saidsecond metal-based foil top surface exposed, said bottom cell surfaceand said second metal-based foil being in electrical communicationthrough electrically conductive joining means.
 14. An article as inclaim 13 wherein said second metal-based foil comprises anelectrodeposit.
 15. An article as in claim 13 wherein said firstmetal-based foil thickness is between 0.001 cm. and 0.025 cm.
 16. Amethod of manufacture of a series interconnected array of photovoltaiccells, comprising:manufacture of photovoltaic cells using roll-to-rollprocessing, said cells comprising thin films of semiconductor materialsupported on a metal-based foil, said cells having a top cell surfaceand a bottom cell surface,a cell width, a cell length and a cellthickness, said cell length being considerably greater than said cellwidth, said cell width defining first and second terminal edges of saidcells, supplying a separately prepared substrate comprising electricallyconductive material regions, said regions having a top surface and abottom surface, joining said bottom cell surface of a first of saidcells to said top surface of a first of said electrically conductiveregions leaving exposed a portion of said top surface of said first ofsaid electrically conductive regions, said joining being accomplishedvicinal said first cell terminal edge, said joining employingelectrically conductive joining means to establish electricalcommunication between said bottom cell surface of a first of said cellsand said top surface of a first of said electrically conductive regions.